The UN ECE R134 regulation is a good requirement to follow as it copies the language in the UN GTR #13 regulation. The updated version of this UN document (UN GTR #13 Phase 2) is currently in approval review at the GRSP in Geneva and should be approved by the end of 2023. Nevertheless, since the US Department of Transportation’s National Highway Traffic Safety Administration is a contracting…

NFPA 2 provides Tables in Chapters 7 and 8 that specify the hazardous area classifications surrounding vent stack outlets. These are based on typical vent systems and flows, but are only applicable for smaller systems. The designer of a vent system should apply the principles of documents such as IEC 60079-10-1 (also required by NFPA 2) or NFPA 497 to evaluate larger vent releases where the…

Guidance for location of vent stacks is provided by NFPA 2, Hydrogen Technologies Code, which also references CGA G5.5, Hydrogen Vent Systems, for additional guidance. Minimum distances to vent stack outlets should be determined from dispersion and radiation analyses. The height of the vent stack and orientation of the release will affect the minimum separation distance.

Dispersion and radiation analysis should be conducted to ensure that the hydrogen cloud will not interfere with the flight path of aircraft. In addition, there may be maximum height requirements due to airport requirements depending on the location of the stack.

Detection systems are nearly always installed but the system design and installation details of detection equipment are up to the manufacturer. Standards are being developed for this market.

Documents such as NFPA 2, Hydrogen Technologies Code, and the International Fire Code have quantity thresholds that differentiate requirements for the design of systems and enclosures. However, even the smaller quantities present a hazard under specific conditions, especially for systems that have the potential to release hydrogen into a confined or unvented space. Good engineering judgement…

All systems must be designed for the applicable operating parameters such as pressure, temperature,
and flow. The sub-cooled liquid hydrogen (sLH2) approach for fueling is comparable to other processes
commonly used to handle cryogenic liquids in the industrial gas industry where remaining gas is
condensed during the fill operation. These processes often operate above the critical…

Hydrogen has been used as a fuel to operate cars, buses, trucks, submarines, aircraft, forklifts, trains and virtually every type of mobile equipment. Each has special considerations which often drive specific requirements for that vehicle type. For example, higher g-loadings of rail operations and operations within tunnels are a couple considerations, but there are no significant barriers…

Each installation should be evaluated based on the results of a hazard analysis considering both of these
scenarios. Separation distances as listed in documents such as NFPA 2, Hydrogen Technologies Code, are
a minimum starting point but may need to be adjusted based on analysis. Recent work by NFPA 2 has
also included overpressure criteria, but the consequences can vary depending on…

Each system should be evaluated for exposure of equipment to jet fires. The design team should develop
a plan to mitigate exposure as part of the hazard analysis. Fire barriers, walls, enclosures, and insulation
systems are frequently installed to meet code requirements where separation distances are not
sufficient or where the probability of exposure to a jet fire is high. Barriers…